Resident Mohammed Abdi said hundreds of residents fled Beledweyne after hundreds of Ethiopian and Somali troops moved in.

Captain Hashi Nor of the Somali military confirmed that Somali and Ethiopian troops had moved in. "I saw Ethiopian troops standing at the doors of neighbouring homes. Somali soldiers are also searching the homes," Mr Abdi said. "Al Shabab retreated back to Bulo Burte and also many of the residents fled, and those who remained are in their homes."

The military movement appears to be a third front against al Shabab, Somalia's strongest militant group.

Kenyan troops moved into Somalia in mid-October in a push against the militants in the country's south. African Union troops from Uganda, Burundi and most recently from Djibouti have mostly pushed al Shabab fighters out of the capital, Mogadishu.

"We are in full control of Beledweyne now and our troops will move forward in the coming hours," Capt Nor, the Somali military officer, said by phone from Beledweyne.

Mr Abdi said the sound of gunfire could be heard in Beledweyne but that he did not believe actual battle was taking place. However, al Shabab on its official Twitter feed said that a battle that began at 6am was still "raging" in the city as of midday.

Al Shabab said that a "majority" of Beledweyne residents joined al Shabab "to thwart the offensive". It claimed that dozens of Ethiopian troops had been killed, but that was impossible to verify and was likely an exaggerated claim.

It later said on Twitter that al Shabab was executing a planned withdrawal and would surround the city.

Somali prime minister Abdiweli Mohamed Ali said in a statement that Somalia's armed forces had taken over "strategic places" from al Shabab in the central region of Hiran. He did not make direct mention of involvement by Ethiopian troops.